Expandable spinal implant

ABSTRACT

An expandable implant device ( 100 ) for insertion between two vertebrae ( 400 ) is disclosed. The device ( 100 ) has an upper body ( 20 ), a lower body ( 40 ) and an external retainer band ( 60 ). The external retainer band ( 60 ) holds the upper body ( 20 ) and lower body ( 40 ) and has an inner surface having a plurality or set of upper ratchet teeth ( 80 U) sloped for allowing upward movement and a plurality or set of lower ratchet teeth ( 80 L) for allowing downward movement. The ratchet teeth ( 80 ) of the upper body ( 20 ) are mated or fitted to the upper teeth ( 80 ) of the retainer band ( 60 ) and the ratchet teeth ( 82 ) of the lower body ( 40 ) are mated or fitted to the lower ratchet teeth ( 82 ) of the retainer band ( 60 ). The height of the device ( 100 ) is increased by upward movement of the upper body ( 20 ) and downward movement of the lower body ( 40 ).

RELATED APPLICATIONS

The present invention is a division of co-pending U.S. application Ser.No. 14/259,639 entitled, “IMPROVED EXPANDABLE SPINAL IMPLANT” filed onApr. 23, 2014.

TECHNICAL FIELD

The present invention relates to spinal implants generally, moreparticularly to an improved expandable spinal implant.

BACKGROUND OF THE INVENTION

Spinal stabilization can be achieved by providing an interbody implant.Some of these implants are bone, PEEK, solid titanium or similarnon-bone implant material and some are hollow implants that provide forinclusion of a bone graft or other suitable material to facilitate bonyunion of the vertebrae.

Interbody implants can be inserted into the disc space through ananterior, posterior or lateral approach. In some systems, the implantsare inserted into a bore formed between adjacent vertebral bodies in thecortical endplates and can extend into the cancellous bone deep to thecortical endplates Implant size is typically selected such that theimplants force the vertebrae apart to cause tensing of the vertebralannulus and other soft tissue structures surrounding the joint space.Tensing the soft tissues surrounding the joint space results in thevertebrae exerting compressive forces on the implant to maintain theimplant in place.

It has been found desirable to keep the surgical opening as small aspractical while still having sufficient room to insert the implantdevice and the end of an elongated tool or insertion instrument.

Advantageously, if the implant size could be reduced further that wouldallow the surgical opening to be reduced; however, once implanted thedevice needs to be expandable to provide sufficient spacing of thevertebrae.

A whole class of expandable interbody implant devices have beendeveloped for this purpose. Some prior art devices use hydraulicexpansion or inflatable balloons. Some devices are stackable elementspiled on themselves to raise their height. Some use rotatable screw jackdesigns. Some are wedges that have a fixed hinged end and an oppositeexpandable end. All of the rotatable expandable devices using screwthreads require the device to be round cylinders or posts.

One of the problems of such devices is the amount of post insertionmanipulation required to reach a fully expanded properly space height istedious and time consuming Secondly, additional set screws or lockingelements are often required to keep the device at its proper size.Thirdly, the devices of a circular shape are not the best fit for theadjacent vertebrae being spaced. Fourth, most of the devices have theinternal space occupied with mechanisms limiting the amount of bonegrowth material available for packing the implants.

The wedge type implants generally contact the bone on an angle andexpandable wedges when expanded simply expand on an angle not parallelto the vertebrae surface. This places localized high loading between thevertebrae because the wedge surfaces are not parallel to the vertebrae.

These and other limitations in the prior art have been corrected andsolved by the present invention as disclosed herein.

SUMMARY OF THE INVENTION

An expandable implant device for insertion between two vertebrae isdisclosed. The device has an upper body, a lower body and an externalretainer band. The upper body has an interior surface forming a hollowcavity and an exterior surface having a plurality of ratchet teethsloped to allow upward movement. The lower body has an interior surfaceforming a hollow cavity and an exterior surface having a plurality ofratchet teeth sloped to allow downward movement. The external retainerband holds the upper body and lower body and has an inner surface havinga plurality of upper ratchet teeth sloped for allowing upward movementand a plurality of lower ratchet teeth for allowing downward movement.The ratchet teeth of the upper body are mated or fitted to the upperteeth of the retainer band and the ratchet teeth of the lower body aremated or fitted to the lower ratchet teeth of the retainer band. Theheight of the device is increased by upward movement of the upper bodyand downward movement of the lower body. The movement is linear andmaintained parallel to the ratchet teeth as the bodies move relative tothe retainer band. The remaining ratchet teeth mated or fitted to theratchet teeth of the retainer are locked to resist compressive movementof the extended upper and lower bodies. The retainer band has at leastone end with a slotted opening. The upper body and lower body are spacedand separated by the retainer band. The vertical movement of the bodiesis parallel and horizontal relative to the vertebrae being spaced. Themovement of the upper and lower bodies increases a hollow cavity size orvolume formed by the retainer band and spaced apart bodies.

Each of the upper body and lower body has a lip at a respectiveoutermost upper surface of the upper body and outermost lower surface ofthe lower body. The lip extends along a peripheral edge of therespective body. The innermost surfaces of the upper and lower bodieshave a stepped edge extending along a peripheral edge. The stepped edgesare abutting or in close proximity when the bodies are fully unexpanded.Preferably, the plurality of ratchet teeth in both the upper and lowerbody extend from the step to the lip along two opposing portions of eachupper and lower body.

The expandable implant has a fully unexpanded height of 10 mm or less.The expandable implant has a fully expanded height of at least 3 mm orpreferably at least 5 mm greater than the unexpanded height.

The retainer band has a plurality of holes between the upper and lowersets of ratchet teeth. The holes are angled to receive a tool todisengage or unlock the mated or fitted ratchet teeth to lower the upperor lower bodies into a retracted unexpanded height. The expandableimplant device further has a separate insertion tool. The insertion toolhas an end sized to fit through said slotted opening of the retainerband and extend toward an opposite end, the tool allows insertion of theimplant device between the two vertebrae to be spaced. The insertiontool has an end sized to fit inside the implant device between the upperand lower bodies. Preferably the end is fixed to a shaft on theinsertion tool. Rotation of the shaft rotates said end into contact withthe upper and lower bodies inside said retainer band and wherein furtherrotation simultaneously moves both upper and lower bodies to an expandedheight. Rotation to a full expansion height occurs at a rotation of 90degrees or more of the end. The height of the expanded device iscontrolled by the number of ratchet teeth passed on movement of thebodies. When the expansion height is set, the upper and lower bodies arelocked automatically relative to the retainer band at the height by therespective remaining mated or fitted together ratchet teeth.

The invention further includes a method of insertion of an expandableimplant device between two vertebrae comprises the steps of: providingan unexpanded implant device, having an upper body, lower body and aretainer band for holding said upper and lower bodies, the retainerhaving a slotted opening; providing an insertion tool having an endsized to fit said slotted opening and fixed to a shaft or handle;inserting the end of the insertion tool into said slotted opening toattach the device to said insertion tool; inserting the device into aprepared surgical opening and between two vertebrae to be spaced apart;rotating the shaft or handle causing the end to rotate into contact withthe upper and lower bodies and continuing said rotation to the desiredheight and stopping rotation locks said device at the height; andreversing rotation of the end to align with the slotted opening andretracting said tool. The method may include packing the implant devicewith bone growth material through said slotted opening. Preferably, themethod further includes the steps of: inserting a wire to the locationbetween the vertebrae where the implant is to be positioned; and guidingthe implant affixed to the insertion tool to the location by passing thewire through the implant, more preferably, wherein the end and the shaftof said insertion tool have a passageway; and inserting said guide wirethrough the end and shaft as well as the implant device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1 is a perspective view of the expandable implant device of thepresent invention.

FIG. 1A is a view showing how the retainer band is deflected to allowinsertion of the upper and lower body into the unexpanded condition.

FIG. 1B is an exemplary tool for unlatching the retainer to allow upperand lower bodies to be assembled to the device in a fully retractedunexpanded condition.

FIG. 2 is a perspective view of the insertion tool of the presentinvention.

FIG. 3 is a perspective view showing the insertion tool end fittedthrough a slotted opening in the retainer band where the upper body isremoved to enable viewing the end inside the implant with the lower endunextended.

FIG. 4 is a view similar to FIG. 3, but where the end has been rotatedshowing the lower portion extended.

FIG. 5 is a perspective view of the implant device extended without theinsertion tool.

FIG. 6 is a cross sectional view of the device taken along line 6-6 ofFIG. 1.

FIG. 7 is a cross sectional view of the device from FIG. 6 wherein theend of the insertion tool is shown rotated expanding the implant device.

FIGS. 8A-8E are views of an exemplary method of using the device in avertebrae repair showing that portion of the spine.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, the expandable implant device 100 madeaccording to the present invention is illustrated. As shown, the implantdevice 100 is in the fully retracted unexpanded condition. As shown, thedevice 100 has an upper body 20, a lower body 40 and a retainer band 60encircling both the upper and lower body. In a preferred embodiment, theupper and lower bodies are made of a plastic or synthetic material. In apreferred embodiment, this material is PEEK (PolyEtherEtherKetone)although alternative materials can be used for either of the upper orlower body. The top outer surface 101 of the upper body 20 and thebottom outer surface 102 of the lower body 40 are provided with aplurality of facets or ridges 103 or roughened surfaces. These surfaces101, 102 will contact the vertebrae when installed and expanded andprovide a gripping surface to which the implant is securely held whenexpanded between the two spaced vertebrae.

As shown, the expandable implant device 100 in the illustrations is asubstantially oblong oval shaped device with straight sides with curvedends. The device can vary in size having a length of 20 to 40 mm,preferably 26 to 34 mm and a height of 5 to 15 mm, preferably 8 to 12mm, in the example about 9 mm. The width of the device is between 8 to15 mm or 8 to 12 mm, as shown 9 mm. While the two sides are illustratedas straight and parallel in their respective lengths, each of the sidescould have an outwardly bowed center increasing the size and surfacearea. Alternatively, the two sides can take on a curved configuration ofa banana shape or parallel crescents along the length to more optimallyfit the space between the vertebrae. All these shapes can employ theinventive features of the device 100.

With reference to the retainer band 60, at one end is shown a slotopening 62 with a circular center 63 cut through the band 60. This slotopening 62 is provided for the insertion tool 200, shown in FIG. 2, toenable its end 202 to slip through and into the implant device 100 up toand including portions of the shaft 204 of the insertion tool 200. Alongthe sides 65, 66 of the retainer band 60 is shown a plurality of holes68 extending on an angle originating partially into a curved depression70 in both an upper portion 67 of the retainer band 60 and a lowerportion 69 of the retainer band. These holes 68 are spaced between slots72 as illustrated. The slots 72 and depressions 70 facilitate retractingthe portions 67, 69 of the retainer band 60 outwardly. A tool 300, shownpartially in FIG. 1B, has ends 302 inserted into one or more of theholes 68 and pried in such a fashion that the portion 67, 69 of theretainer 60 can flex outwardly. When both sides 65, 66 of the retainerband 60 have these portions flexed outwardly, as shown in FIG. 1A, thebody portion either upper body 20 or lower body 40 can then be insertedfully into the retainer band 60. This enables the implant device 100 tobe pre-assembled in a fully retracted condition. This fully retractedposition is also illustrated in the cross sectional view FIG. 6. Asshown in FIG. 6, the top upper surface 101 and bottom lower surface 102of the respective upper and lower bodies have a lip 107, 108 which comesinto close proximity or contact with the retainer band 60. Accordingly,when fully seated, the implant 100 is at its lowest possible verticalheight (H_(U)). This fully retracted position creates a very low profileimplant device that enables the device 100 to be slipped into a smallersurgical opening than otherwise would be possible.

As shown in FIG. 3, which has the upper body 20 removed so that theinsertion tool 200 and end 202 are clearly visible, it is important toobserve that the insertion tool 200 when slipped into the implant device100, as shown, extends fully into the opposite end of the implant device100. As shown in FIG. 5, where the insertion tool 200 is removed, acircular opening 64 at the opposite end of the device 100 creates anaperture through which the shaft end 204A of the insertion tool 200 canbe inserted. This stabilizes the tool 200 so that upon rotation of theshaft 204, the end 204A can also properly rotate in a uniform fashion sothat it is parallel to both the upper body 20 and lower body 40 at thetimes of rotation. As can be appreciated in FIG. 3, the retainer band 60along its sides 65, 66 has a plurality of ratchet teeth 80, 82. In FIG.6 these ratchet teeth 80, 82 are provided on both sides of the retainerband 60 on an upper portion 67 and a lower portion 69 of the retainerband 60, those on the upper portion 67 being a set 80U, those on thelower portion being a set 80L.

With reference to FIG. 6, it is important to note in the cross sectionalview that the retainer band 60 has two sets of ratchet teeth 80, 82, anupper set 80U along each side has the teeth sloped in a direction suchthat the teeth 80 allow the implant device 100 upper body 20 to freelymove in an upward or outward direction and the lower set 80L teeth 82are sloped in such a fashion that the lower body 40 can be pushed in anoutward or downward direction with ease. These sets of ratchet teeth 80,82 enable the upper body 20 and lower body 40 to move simultaneouslyupon rotation of the insertion tool 200. This rotation is best shown inFIG. 6 in the retracted position where the end 202 is shown in agenerally horizontal position and both upper and lower bodies 20, 40 areshown in the fully retracted position. FIG. 7 shows the end 202 of theinsertion tool 200 has been rotated approximately 90 degrees wherein theupper body 20 and lower body 40 have been moved outwardly, the upperbody 20 moving in an upward direction and the lower body 40 moving in adownward direction. This increases the effective or expanded height(H_(E)) of the device 100 substantially. The device can be moved inincrements as low as one ratchet tooth 80, 82 which corresponds to anincrease in size of fractions of mm's to as much as 5 mm or more in afully expanded height (H_(E)) condition. In the fully expanded conditionof FIG. 7, the remaining mated or fitted ratchet teeth 80, 82 betweenthe retainer band 60 and the upper or lower body 20, 40 hold the device100 into position. It is important to note, the teeth 80, 82 aredesigned in such a fashion that they freely allow an outward movementrelative to the retainer band 60, but resist any inward movement bycompressive forces due the shape of the teeth which can move in oneoutward direction only based on the configuration of the teeth surface.The teeth surface being either inclined slightly inwardly or at aminimum flat, in such a fashion that the teeth 80, 82 cannot moveinwardly unless the retainer band 60 is flexed outwardly as previouslydescribed using an external tool 300 into the sloped hole openings 68 tobend the retainer band sides 65, 66 outwardly so the body 20 or 40 canbe retracted. During normal use, it is unnecessary to move the implantdevice 100 vertically down as the surgeon when installing the device 100already in the retracted position will simply bring the implant 100 toits proper location between the two spaced vertebrae and will rotate theshaft 204 while doing so expand the device 100 to the position at whichhe wants the vertebrae to be spaced. Once this occurs, the handle orshaft 204 can be reverse rotated or relaxed in such a fashion that theend 202 is no longer pushing against the interior surface of either theupper body 20 or lower body 40.

As shown in FIGS. 6 and 7, it is important to note that around theperipheral inward innermost surfaces of the upper 20 or lower 40 body isa step configuration. This step configuration 22, 42 provides a workingsurface 23, 43 around the entire peripheral interior of the upper bodyand lower body. This enables the insertion tool end to push against thesurfaces 23, 43 as it is lifting or pushing downwardly the respectivebody 20 or 40. Because of the stepped configuration, the surfaces 23, 43provided ensure the end 202 of the insertion tool 200 is always incontact with the upper and lower body during this rotation, if not alongthe sides as it is initially lifting up, at least at both ends of thebodies 20 or 40 as the insertion tool 200 end 202 is rotated in analmost vertical condition as shown in FIG. 7. It is important note inFIG. 6, that the space between the upper body 20 and lower body 40between the interior surfaces form a hollow cavity 140 into which notonly the end 202 of the insertion tool 200 can be inserted, but bonegrowth material can be inserted either on a preassembly into the deviceor preferably after the expandable implant device 100 has been insertedinto the spine. As shown in FIGS. 1 and 6, the implant device 100 upperbody 20 and lower body 40 has an oval opening at the top and bottom.This oval opening provides easy packing of the bone growth material onpreassembly, however, once assembled these areas are blocked by thevertebrae. Accordingly, when the insertion tool is removed, the cavity140, as shown in FIG. 7 in the expanded condition, is enlarged greatlyresulting in the volumetric space being increased dramatically, by theexpansion of the implant device 100. When this occurs, additional bonegrowth material or all the bone growth material can be inserted when theinsertion tool 200 is removed. Once the insertion tool 200 is removed,the bone growth material (not shown) can fully pack the implant device100 through the slotted opening 62 and is in direct contact with thesurface of the vertebrae through the oval openings of the cavity 140 atthe top surface 101 and bottom surface 102. It is important toappreciate that the ratchet teeth 80, 82 on each body that extend fromthe peripheral step 22, 42 to the lip 107, 108 on each upper or lowerbody 20, 40 and are designed so that the slope permits the propermovement. The complimentary or mating teeth of the retainer band 60 aresimilarly sloped. This enables the device 100 to fully expand withminimal resistance; however, they block any retraction and lock thedevice 100 against any compressive load tending to move the device upperbody 20 or lower body 40 inwardly. This automatic locking feature is agreat advantage in that no additional tools, set screws or othermechanical instruments are required. Once the device 100 is inserted andthe insertion tool 200 is rotated moving the implant 100 into itsexpanded position and the insertion tool 200 is then reverse rotatedback to its horizontal position so that it can be withdrawn through theslotted opening 62, the manipulation is complete. The outward movementis facilitated by the sloped teeth surface acting as a ramp, typicallyless than 30 degrees off vertical, preferably 20 degrees or less. Theinward movement is blocked by the opposite tooth surface being orientedhorizontal at 90 degrees or less than 90 degrees off vertical socompressive forces pushing the bodies inwardly are stopped or evensloped directionally to increase the bite and oppose any lateraldetaching forces.

With reference to the insertion tool 200, it is noted that the insertiontool 200 can have a hollow hole 500 extending all the way through theshaft 204 from one end to the other. This hollow hole 500 provides ameans or access for which a K wire can be slipped through the insertiontool 200 and the implant device 100. During the surgical procedure, itis preferable that the insertion tool 200 is fully inserted into theimplant device 100 and that a pre-inserted K wire that has been placedin the location where the implant device 100 is to be directed to itspreferred position in between the vertebrae in such a fashion that asthe surgeon inserts the implant device 100 with the insertion tool 200securely holding the device 100, he may then be guided to the properlocation by use of the K wire. To further this procedure, applicantshave provided FIGS. 8A-8E showing some of the actual insertion steps ofan implant device insertion.

As illustrated in FIG. 1, the expandable implant device 100 has twoopposing longitudinal extending outer surfaces with gripping facets 103each defining ridged surfaces 101, 102. The ridged gripping surfaces101, 102 are meant to assist with the implant's ability to grip theadjacent bone structure. In one aspect, the ridges are angled in orderto assist in preventing the implant from backing out.

Sometimes, it is beneficial to have the means with which to promote bonegrowth and/or fusion. In one aspect, the implant device 100 furtherdefines an implant cavity 140 in communication with the implant apertureand substantially open to at least one, or both, of the grippingsurfaces 101, 102. In this aspect, bone graft material or bone cementcan be introduced into the implant cavity 140. The bone graft materialcan be, for example, autologous bone, allograft bone, bone substitute,osteoinductive agents, and the like.

The implant 100 itself comprises a biocompatible material, capable ofbeing inserted into the body. In one aspect, the bio-compatible materialfor the upper and lower body is selected from the group consisting ofPolyEtherEtherKetone, ceramic, allograft bone, and PolyEtherEtherKetonewith BaSO₄. Other biocompatible materials are also contemplated. Theretainer band is preferably made of titanium. To facilitate a betterunderstanding of how the present inventive expandable implant can beused, exemplary methods of the procedure are provided. These methods areas described in U.S. Pat. No. 8,496,709 entitled “Spinal Implant”granted on Jul. 30, 2013 and commonly owned by assignee Amendia, Inc. ofAtlanta, Ga.; the contents of which are incorporated herein by referencein its entirety.

Also presented herein is an exemplary percutaneous fusion method tocorrect disc compression. The method, in one aspect illustrated in FIGS.8A-8E, comprises making a posterolateral incision to access the desiredspinal motion segment; determining a target level of the disc space 402between adjacent vertebral bodies 400 for implantation of an implant;locating a path to the disc space at the target level; inserting a guidewire 440 to maintain a path to the disc space 402; sliding the spinalimplant along the guide wire 440 to position it into the disc space atthe desired position; removing the guide wire; and fixating at least aportion of the desired spinal motion segment.

This first step comprises making a posterolateral incision to access thedesired spinal motion segment. In one aspect, the initial access pointcan be made through Kambin's Triangle 410 Kambin's Triangle, as thoseskilled in the art will appreciate, is the site of surgical access forposterolateral endoscopic discectomy. It is defined as a right triangleover the dorsolateral disc. The hypotenuse is the exiting nerve, thebase (width) is the superior border of the caudal vertebra, and theheight is the traversing nerve root.

The method also comprises determining the target level of the disc spacebetween adjacent vertebral bodies 400. Once the target level isestablished, the method comprises locating a path to the disc space atthe target level. This can be accomplished, for example, using a nervemonitoring probe 420 with a transfer sleeve 430. The nerve monitoringprobe can measure the proximity of the exiting nerve root. Oncemeasured, in an exemplified aspect, the probe 420 can then be removed,leaving the transfer sleeve 430 in place. In one aspect, the nervemonitoring probe comprises an EMG Navigation system, comprising ablunt-tipped monopolar probe and an exchange cannula.

The method also comprises inserting a guide wire through the transfersleeve to maintain a path to the disc space. In one aspect, the guidewire 440 can be a Kirschner wire or k-wire. After insertion of the guidewire, one aspect of the method comprises removing the transfer sleeveand placing a dilator 450 over the guide wire. The dilator 450 can bedriven into the disc space 402 to distract the vertebral bodies 400.

In one aspect, the next step comprises positioning an access portal 460into the disc space. For instance, in one exemplified aspect, thesurgeon can slide the access portal 460 over the dilator and use animpact sleeve with a mallet to lodge the portal into the disc space. Thedilator and guide wire can then be removed, leaving the access portal inplace.

In a further aspect, the method can comprise performing a discectomy anddecorticating the vertebral endplates. In an exemplified aspect, a drillcan be used to access the nucleus and prepare the area for otherdiscectomy instruments. For example, and not meant to be limiting, adisc shaper, can be used for endplate preparation. The surgeon may electto remove some of the loose disc material at this point. As such, apituitary rongeur can be used. In another aspect, a disc cutter can beused to accomplish a thorough discectomy. After which, the pituitaryrongeur can be used again to remove remaining disc remnants

In one aspect, a bone graft (not shown) can then to be introduced. Asone skilled in the art can appreciate, this can be accomplished throughthe portal using a tube and plunger system. In one aspect, the bonegraft is a sentinel bone graft. The surgeon can then re-introduce theguide wire 440 and remove the access portal 460.

With input from pre-surgical radiographic film, the next step cancomprise determining the height of an adjacent level healthy disc toassist with the selection of the proper amount implant. The size of theimplant 100 can be easily determined avoiding the need to be confirmedwith a paddle trial or a solid body trial. In the U.S. Pat. No.8,496,709; to do so, the surgeon had to first insert the trial implantalong a path, guided by the guide wire. An insertion tool 200, asdescribed herein above, had been used. Once inserted, if the selectedtrial implant cannot be rotated into an erect position, the surgeoncould then step down to a smaller size. Alternately, if the selectedtrail can be rotated into an erect position without much frictionalresistance, the surgeon could choose the next larger size. Severaliterations were necessary to achieve the correctly sized implant. In thepresent invention using the expandable implant, this procedure isunnecessary, saving much time.

As described herein above, in one aspect, the implant 100 comprises animplant cavity 140. As such, the method comprises, after determining theappropriate implant height, loading graft material into the implantcavity and connecting the implant to the insertion tool and followingthe guide wire to insert the implant. Imaging technology can be used toverify the correct location of the implant. In one aspect, fluorographicimaging can be used to watch radiographic markers in order to determinethe correct location of the implant. In one aspect, as determined by thesurgeon, when the images show the radiographic markers evenly placed oneach side of the spinous processes, the implant is placed properly. Oncethe implant is placed properly, the surgeon can then rotate theinsertion tool up to 90 degrees or more expanding the implant device tothe desired height and release it from the insertion tool 200.

As illustrated, the sets of ratchet teeth 80U, 80L extend lengthwise inparallel rows of teeth 80, 82 so as the upper body 20 and lower body 40move relative to the retainer 60, the movement ratchets outwardly toothby tooth in a controlled and maintained parallel relationship to thelength of the teeth avoiding or preventing any angular tilting orcocking. This insures the expansion of the bone contacting outersurfaces 101, 102 is accomplished uniformly, evenly and simultaneously.While the direction or path of the movement is clearly perpendicular tothe length of the teeth.

Variations in the present invention are possible in light of thedescription of it provided herein. While certain representativeembodiments and details have been shown for the purpose of illustratingthe subject invention, it will be apparent to those skilled in this artthat various changes and modifications can be made therein withoutdeparting from the scope of the subject invention. It is, therefore, tobe understood that changes can be made in the particular embodimentsdescribed, which will be within the full intended scope of the inventionas defined by the following appended claims.

What is claimed is:
 1. A method of insertion of an expandable implantdevice between two vertebrae comprises the steps of: providing anunexpanded implant device, having an upper body, lower body and aretainer band for holding said upper and lower bodies, the retainerhaving a slotted opening; providing an insertion tool having an endsized to fit said slotted opening and fixed to a shaft or handle;inserting the end of the insertion tool into said slotted opening toattach the device to said insertion tool; inserting the device into aprepared surgical opening or between two vertebrae to be spaced apart;rotating the shaft or handle causing the end to rotate into contact withthe upper and lower bodies and continuing said rotation to the desiredheight and stopping rotation locks said device at the height; andreversing rotation of the end to align with the slotted opening andretracting said tool.
 2. The method of insertion of an expandableimplant device between two vertebrae of claim 1 further comprisespacking the implant device with bone growth material through saidslotted opening.
 3. The method of insertion of an expandable implantdevice between two vertebrae of claim 1 further comprises the steps of:inserting a wire to the location between the vertebrae where the implantis to be positioned; and guiding the implant affixed to the insertiontool to the location by passing the wire through the implant.
 4. Themethod of insertion of an expandable implant device between twovertebrae of claim 3 wherein the end and the shaft of said insertiontool have a passageway; and inserting said guide wire through the endand shaft as well as the implant device.